Fraser has been out injured for Newcastle, not playing since Scotland’s 4-0 win over the Faroe Islands on March 31, a game in which he scored.
And while he has not kicked a ball for United for nearly two months, he is, however, expected to be named in the Euros squad when Clarke drops his 26-man list tomorrow.
Bruce believes it is a ‘gamble’ taking the former Bournemouth man, who has been in and out all season due to injury.
Speaking ahead of the Magpies’ game against Sheffield United tomorrow evening, Bruce said: "As for Ryan, it has been a difficult time for him.
“He does desperately need a pre-season. Pre-season will be huge for him.
“Whether he is going to be picked in the Scotland squad, I think that would be a gamble as he has not played the last six or seven weeks.
“He has had no real football football or trained (in that time).
“Pre-season will be key for him. He didn't have a pre-season the year before and last season's was a non-entity really.
“The same goes for Isaac (Hayden) and Jamaal Lascelles – it is key for all of them.”
This summer is the first time in a generation Scotland have qualified for a major tournament – and it is unlikely Aberdeen-born Fraser will want to miss out.